This invention relates to perpendicular magnetic recording, and particularly to reduction of noise in the recording to improve signal-to-noise ratio during read operations.
Perpendicular recording is a form of magnetic recording in which the magnetic flux of recorded data are oriented perpendicularly to the surface recording medium, as opposed to longitudinally along a track of the medium as in traditional longitudinal recording. Perpendicular recording offers advantages over longitudinal recording which may be important to extend disc drive technology beyond data densities of 100 gigabytes per square inch. Two of the important advantages of perpendicular recording over longitudinal recording are (1) the ability to achieve significantly higher linear densities and (2) larger writing fields. Higher linear densities are achieved because the demagnetization energy in the magnetic transitions in perpendicular media supports the recorded transitions, as opposed to deteriorating the transitions as in longitudinal recordings. Larger writing fields are a result of the use of a soft magnetic underlayer beneath the hard recording layer of the medium.
However, the soft magnetic underlayer often generates noise during playback which can be detrimental to the implementation of perpendicular recording in disc drives. Computer models of the flux patterns of perpendicular recording shows that even if flux in the soft underlayer is perfectly aligned at the beginning of a write operation, the write process generates ripple structures, or distortion, in the recorded magnetic pattern that increase over the duration of the writing cycle. These magnetic distortions are read as noise and will deteriorate the signal-to-noise ratio of the readback. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
One embodiment of the invention is a perpendicular recording head for transferring data to a magnetic medium having a recording layer and an underlayer of soft magnetic material. Erasing means erases magnetic effects in the soft magnetic material underlayer. In preferred embodiments, a head includes a first write transducer for perpendicularly writing data into the recording layer, and the erasing means comprises a second write transducer for writing a DC effect longitudinally into the underlayer.
In preferred embodiments, the head has an air bearing surface arranged to confront the magnetic medium and the second write transducer includes first and second permanent magnet legs supported by the head in spaced relation to form a transducing gap. The first and second legs are arranged to generate a magnetic field along the track of the magnetic medium to write a DC magnetic effect longitudinally into the soft magnetic underlayer.
In use, data are perpendicularly written into the recording layer of the medium by the first write transducer, and longitudinal magnetic effects are erased from the soft magnetic underlayer by the second write transducer. As a result, noise recovered by the read transducer is reduced.
Other features and benefits that characterize embodiments of the present invention will be apparent upon reading the following detailed description and review of the associated drawings.